Monthly Archives: December 2014

One of my science teacher heroines is Ms. Frizzle from the magic school bus. Remember her teaching philosophy?

I need a poster of this in my room so I can point to it when my students ask their favorite question; “is this right?” This question hurts my soul for a few reasons…

1. Students just want a yes or no answer

2. There is no emphasis on the process, just the answer

3. The question is usually accompanied by the statement “I don’t want to be wrong”

Somewhere along the way we taught students that it is not okay to be wrong. At some point we told students that the process doesn’t matter, you only get credit for the final answer. Most importantly, we taught students that it is not okay to make mistakes. Ms. Frizzle would be seriously disappointed.

Modeling instruction helps me battle the dreaded “is this right?” question by simply never answering it. I reply to every question with another question. I always start with “I don’t know, what do you think?” so the student is forced to explain his or her reasoning. If there are blatant errors, I may pinpoint a particular spot and ask “why did you do this?” If there are no errors I might ask “are you confident in your reasoning?” I never give a “yes” or “no” answer.

Standards-based grading allows students to make mistakes on assessments and be given a second chance… and a third chance…. and a fourth chance…. and even a twentieth chance if it comes to it! Students are assessed multiple times on a single learning target and always have the opportunity to initiate their own reassessments. Students are not penalized for learning at different paces as long as they learn. That is the objective after all.

These two strategies together have helped shift the culture in my classroom from one of rote memorization to genuine learning. Do students still ask “is this right?” Of course they do. Now I just sit back and smile as another student in the room answers before I can, “I don’t know, what do you think?”

I asked my students this year “what is inside the bubbles of boiling water?” Without hesitation, all 24 students in my advanced chemistry class answered “hydrogen and oxygen gas.” These students were sure of their answer because they knew that water is made of hydrogen and oxygen.

A typical chemistry class is taught from the top down; you start with the most complicated model of the atom and go from there. Do you really need the electron-cloud model of the atom to understand the gas laws? What about thermodynamics? What about bonding? Yes, I teach bonding without the electron-cloud OR Bohr model! The boiling water misconception is why.

My chemistry class starts with the Democritus model: everything is made of particles. This does not mean everything is made of atoms. Students may describe air particles, water particles, desk particles and even students particles. We use this model to explore mass, volume, and density. Then we observe diffusion and infer that particles must be moving and particle speed corresponds to particle temperature. This inference allows us to explain the gas laws and thermodynamics.

Let’s stop here for a second. If my students had no prior knowledge and I asked them “what’s inside the bubbles of boiling water?” at this point in our curriculum, they certainly would not answer “hydrogen and oxygen gas.” They would think more simply and answer “water gas particles.” Misconception averted.

Continuing on, after finishing our thermodynamics unit, the students observe water being broken into two separate gases in the Hoffman apparatus and must infer there is something smaller than a water particle. Those smaller particles can somehow “hook” together to form new substances. This is the Dalton model. We use the Dalton model to explore mixtures and pure substances as well as the Laws of Definite and Multiple Proportions.

Next, the students observe electrostatic attraction and must infer that particles have a mobile negative charge. This is the Thompson plum pudding model. This model gets my students through bonding. We talk about bonding in terms of attractions and physical properties instead of anthropomorphizing the octet rule. The Thompson model takes us through moles, chemical reactions and stoichiometry.

It is not until the end of the year that we observe graphs of ionization energies to infer that electrons exist in different energy “levels” which leads us to the Bohr model. My students then leave my classroom with a deep conceptual understanding of chemistry and how the world works at the particle level as opposed to a disjointed collection of equations and rules.

Chemistry was not discovered by reading textbooks so why should we teach it that way?

I cannot take credit for any of this. This concept was developed by the wonderful people at Arizona State University and is part of the Modeling Instruction curriculum. Find a workshop near you this summer at modelinginstruction.org.